Korea and Japan use wheat from Oregon, Washington and Idaho to make noodles, sponge cakes and crackers. They are opposed to importing genetically modified food.

The U.S. Agriculture Department is investigating the discovery of the wheat, which is not approved for farming in the United States. The department has said it appears to be an isolated incident.

Agriculture Department officials have said the wheat is the same strain as a genetically modified wheat that was designed to be herbicide-resistant and was legally tested by seed giant Monsanto a decade ago but never approved.